Fluidic constant bias differential signal generator

ABSTRACT

A constant-bias differential fluidic signal generator. A zerobias differential fluidic signal is summed with a constant but adjustable bias signal. The zero-bias differential signal is generated by two signals that increase and decrease proportionately and simultaneously as a function of a control pressure. Such signals can be generated with a fluidic aspirator that creates a vacuum signal in proportion to an applied pressure signal. If the transfer characteristic of such an aspirator is linear with unity gain, the bias of the differential signal generated thereby would be zero. The two signals generated by the aspirator are combined with a constant-bias signal through a pair of passive summing junctions. This provides not only a constant bias level but one which is independently adjustable by means of the constant-bias signal level, thereby rendering the device very valuable in the testing of fluidic components and systems.

United States Patent [191 Woods June 28, 1974 F LUIDIC CONSTANT BIAS DIFFERENTIAL SIGNAL GENERATOR Robert L. Woods, Kensington, Md.

[73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

22 Filed: Mar. 7, 1973 211 App]. No.: 338,786

[75] Inventor:

[52] US. Cl. 137/816 [51] Int. Cl. F15c 1/00 [58] Field of Search 1'37/803-842 [56] References Cited .UNIIEQ5IAIES PATENTS..-

5/1966 Colston 137/818 X 3/1970 Rainer 137/319 X 3/1970 Doherty 137/818 Primary Examiner-William R. Cline Attorney, Agent, or Firm-Edward J. Kelly; Herbert Berl; Saul Elbaum [5 ABSTRACT two signals generated by the aspirator are combined with a constant-bias signal through a pair of passive summing junctions. This provides not only a constant bias level but one which is independently adjustable by means of theconstant-bias signal level, thereby rendering the device very valuable in the testing of fluidic components and systems.

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. 1 v FLUIDIC CONSTANT BIAS DIFFERENTIAL SIGNAL GENERATOR RIGHTS OF GOVERNMENT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a fluidic signal generator and, more particularly, to a fluidic signal generator for providing a constant bias adjustable differential fluidic 2. Description of the Prior Art In the testingof fluidic components and systems, it is often desirable to generate a differential fluidic test signal which has a constant bias level, inasmuch as the bias level effects the gain and linearity of an amplifier. This would require one of the differential signals to decrease proportionately to the increasing of the other signal. It is further desirable to have available an independently adjustable bias level so that the effect of the bias level on the operation of the amplifier can be studied. Most methods previously used for testing fluidic components and systems employ a coupling between the bias level and the differential signal. This makes the two interdependent and-prevents the independent adjusting of one with respect to the other so that their different effects on amplifier operation can be observed and studied.

It is therefore a primary object of the present invention to provide a device that generates differential fluid signals that have a constant but independently adjustable bias level.

Another object of the present invention is to provide a fluidic constant-bias differential signal generator that has no coupling between the differential signal and the bias level. v

. A further object of the present invention is to provide in a fluidic constant-bias differential signal generator means for generating a pair'of differential signals one of which decreases'proportionately to the increase of the other as a function of the supply pressure.

A'further object of the present invention is to provide a fluidic signal generator whose bias level is independently adjustable to a constant level for the particular characteristics of the fluidic devices under test.

SUMMARY OF THE INVENTION Briefly, in accordance with the invention, a constant- .bias differential fluidic signal generator is provided which comprisesmeans for generating a zero-bias differential fluidic signal, means for generating a constantbias fluidic signal, and means for summing the zero-bias signal with the constant-bias signal to provide the desired result. The zero-bias differential fluidic signal is generated in a preferred embodiment form by a fluidic aspirator that creates a vacuum signal in proportion to its applied pressure signal. Each of these proportionately increasing and decreasingvsignals are summed with a constant-bias signal in a pair of passive summing junctions. Fluidic resistances are provided in the legs of the summing junctions to provide proper isolation between the signals. The output of the generator provides a constant bias level differential fluidic signal wherein further the bias level is adjustable for the particular devices under test.

BRIEF DESCRIPTION OF THE DRAWING The specific nature of the invention as well as other objects, aspects, uses, and advantages thereof will clearly appear from the following description and from the accompanying drawing, in which:

FIG. 1 is a schematic representation of the geometry of a fluidic aspirator utilized in a preferred embodiment of the present invention;

FIG. 2 is a combined graph that illustrates the characteristics of a typical fluidic aspirator such as that depicted in FIG. 1;

FIG. 3 is a schematic representation of the aspirator of FIG. 1;

FIG. 4 illustrates a graph of the expected output pressure verses the input pressure of the aspirator of FIG.

FIG. illustrates a preferred embodiment fluidic circuit utilized for summing the aspirator output with a constant bias signal; and

FIG. 6 illustrates typical test results ofthe circuit of FIG. 5 in which the constant but adjustable bias level of the output is illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENT The basic concept involved in a preferred embodiment of the device of the present invention is to sum a zero-bias differential signal with a constant but adjustable bias signal so as to produce a constant biasdifferential fluidic signal with adjustable bias level. The zero-bias differential signal is made up of two signals which increase and decrease simultaneously as a func' tion of a control pressure and the two signals may be referred to as differential signals. The differential signal can be generated by a fluidic aspirator of FIG. 1 that creates a vacuum signal P in proportion is its applied pressure signal P. In FIG. 1 the control pressure signal P is provided at port 14 to feed through power nozzle 22 to interaction region 19. Located on either side of interaction region 19 are aspiration ports 16 and 18. The flow of the supply signal through interaction region 19 creates a vacuum signal P at port 12 that is of equal magnitude but of opposite polarity to the applied pressure signal P. The diffuser 20 receives the supply pressure signal and the aspirated signal and, for the purposes of the present invention, is vented to the atmosphere. FIG. 2 shows the characteristics of a typical aspirator such as that depicted in FIG. 1. The combined plot of FIG. 2 shows the blocked load transfer characteristics (P' vs. P*); the aspirated pressure flow characteristics (Q vs. P) for constant supply pressure, P; and the supply characteristic (Q vs. P). The blocked load transfer characteristic is represented by line 42; the aspirated pressure flow characteristics are represented by lines 44; and the supply characteristic is represented by lines 38 and 40 for the two cases of the aspiration blocked and the aspiration open, respectively. The critical dimensions of the aspirator of FIG. 1 that was utilized to achieve the resultant characteristics of FIG. 2 were as follows: power nozzle width 22 W 0.020 in., element depth 4W, aspiration port widths 38 2W, diffuser entrance width 24 1.6W, diffuser 20 length 25W, and diffuser 20 angle 6. This aspirator has a blocked load transfer gain of 1.0

(i.e., for 1.0 lbs/in pressure, 1.0 lbs/in vacuum is generated). FIG. 3 illustrates the schematic representation of the aspirator of FIG. 1 wherein 34 represents the supply pressure line, 32 represents the aspirated pressureline, and 36 represents the diffuser.

By using the supply pressure to the aspirator 30 as P and the vacuum signal generated by aspirator 30 as P, two diverging signals will be generated as shown by FIG. 4. Since the transfer characteristic of the aspirator 30 is linear with unity gain, the bias (average value of P and P) of the differential signal will be zero.

The preferred embodiment for the circuit utilized for summing the differential signal from the aspirator and the constant-bias signal generated by an independent input 48 consists of a pair of passive summing junctions 67 and 69 as shown in FIG 5. The differential signals P and'P are introduced via legs 46 and 42 respectively to the summing junctions 69 and 67, respectively. The constant-bias signal is connected from a common supply 48 to the summing junctions 69 and 67 via legs 50 and 49, respectively. If negative bias signals were desired, the bias input 48 could be replaced by another fluidic aspirator. In the circuit of FIG 5, two summing resistors R1 and R2 are about the same value and the shunt resistor R3 is about one-tenth of R1 to provide proper isolation between signals. The value of the fluidic resistances R1 should be sufficiently high so that 8.0 lbs/in is attenuated to the maximum test level desired. The foregoing pressure represents the saturation level of the aspirator described in FIG. 1. The input impedance of the device under test that is connected to outputs 64 and 66 could be used as the shunt resistor R3. Another fluidic resistor R is added to the positive side in leg 46 to help match the output impedances of the differential signals.

FIG. 6 illustrates experimental characteristics generated by the circuit of FIG. 5. Two bias levels represented by lines 72 and 74 were obtained in two different experiments. Bias line 74 is that of zero-bias with no constant bias signal introduced at bias input 48 of FIG. 5. Bias line 72 represents a 0.1 lbs/in bias introduced through bias supply 48 of FIG. 5. In experimental results, the bias levels 72 and 74 were constant within 3 percent of the differential signal. Improvements will obviously result with a more linear aspirator characteristic. The dynamic range of the circuit of FIG. is very high, about 500.

It is seen that by virtue of the foregoing, I have provided a constant bias differential fluidic signal source which makes possible precisely defined testing of fluidic amplifiers to produce static characteristics in a consistent manner. Bias of the input signals has a profound effect upon the amplifier gain characteristics. Testing with inconsistent bias signals will produce nonrepeatable results. It is the foregoing problem towards which the instant invention was advanced.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim as my invention:

l. A differential fluidic generator comprising in combination:

a fluidic aspirator means for generating a vacuum signal which increases and decreases proportionately and simultaneously with a respective variation of a control pressure fluid signal;

means for generating a biassing fluidic pressure signal; and

means for summing said vacuum signal with said biassing fluidic pressure signal and said control pressure fluid signal with said biassing fluidic pressure signal, and for providing output signals representative of said summations.

2. The generator of claim 1 wherein said aspirator comprises an input port and an output port, said control pressure fluidic signal being applied to said input port and wherein said vacuum signal appears at said output port.

3. The generator of claim 2 wherein the transfer characteristic of said aspirator is linear with a gain of unity.

4. The generator of claim 3 wherein said means for summing comprises first and second passive summing junctions, each having two inputs and a single output.

5. The generator of claim 4 wherein said two inputs to said first summing junction comprise said vacuum signal and said biassing fluidic signal.

6. The generator of claim 5 wherein said two inputs to said second summing junction comprise said control pressure fluidic signal and said biassing fluidic signal. I

7. The generator of claim 6 further comprising means for providing isolation between the output signals of said first and second summing junctions.

8. The generator of claim 7 wherein said isolation providing means comprises first and second fluid resistors located in the paths of each of said two inputs to said passive summing junctions and a third shunt fluid resistor.

9. The generator of claim 1 wherein the amplitude of said biassing signal may be varied. 

1. A differential fluidic generator comprising in combination: a fluidic aspirator means for generating a vacuum signal which increases and decreases proportionately and simultaneously with a respective variation of a control pressure fluid signal; means for generating a biassing fluidic pressure signal; and means for summing said vacuum signal with said biassing fluidic pressure signal and said control pressure fluid signal with said biassing fluidic pressure signal, and for providing output signals representative of said summations.
 2. The generator of claim 1 wherein said aSpirator comprises an input port and an output port, said control pressure fluidic signal being applied to said input port and wherein said vacuum signal appears at said output port.
 3. The generator of claim 2 wherein the transfer characteristic of said aspirator is linear with a gain of unity.
 4. The generator of claim 3 wherein said means for summing comprises first and second passive summing junctions, each having two inputs and a single output.
 5. The generator of claim 4 wherein said two inputs to said first summing junction comprise said vacuum signal and said biassing fluidic signal.
 6. The generator of claim 5 wherein said two inputs to said second summing junction comprise said control pressure fluidic signal and said biassing fluidic signal.
 7. The generator of claim 6 further comprising means for providing isolation between the output signals of said first and second summing junctions.
 8. The generator of claim 7 wherein said isolation providing means comprises first and second fluid resistors located in the paths of each of said two inputs to said passive summing junctions and a third shunt fluid resistor.
 9. The generator of claim 1 wherein the amplitude of said biassing signal may be varied. 